Control system for heating



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CONTROL SYSTEM FOR HEATING Filed July 5, 19:54 7 Sheets-Sheet :s

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CONTROL SYSTEM FOR HEA TING Filed July 5, 1934 7 Sheets-Sheet 7 Patented Dec. 2c, 1939 UNITED STATES PATENT OFFICE 1'! Claims.

The present invention relates generally to control means for heating systems and the like and has for its principal purpose the provision of control means so constructed and arranged as to se- 5 cure a greater degree of uniformity and comfort than hitherto has been possible, particularly in automatic systems, such as those fired by gas or oil.

There are a number of factors involved in the problem of securing uniformity of temperature and comfortable conditions when using automatic heating. To illustrate, when automatic heating such as with gas or oil is used in a hot water heating plant, for example, the intermittent firing of the boiler or furnace may cause the radiators to become warm for a period, then the radiators of the heating medium therein, may cool down to approximately room temperature for a time, even while the temperature of the room as registered by the thermostat is still at or above the thermostat setting, and then the next operation of the furnace will raise the temperature of the medium within the radiators to a point considerably above room temperature, producing relatively wide variations in the temperature of the heating medium.

In automatic heating, one of the most generally used controlling means embodies a thermostat situated in the room or the space to be heatedv and operatively connected with the boiler, furnace, or other source of heat, in such a way that when the room falls to a given temperature, say '10", the source of heat is placed in operation, and'when the room temperature increases to a ting, say 72, the furnace or burner is cut off.

variations mentioned above are introduced intothe heating medium. that is, the medium which 4 transfers the heat from the burner or boiler or other heat sour-m to the radiators or other heat disslpatingmeans in-the room. and these temperature variations frequently vary over a redatively wide range,

thermostat. even in the instrument itself, and in such a system as referred to above. wide variations mentioned above are accentuated by the inherent lag in the system. Consider arsituation where the burner is started when the room point, slightly above the first temperature set- There is inherent ins in he operation of n temperature drops to 70 and is shut oil when the room temperature has increased to 72. During the time that the room temperature is thus increased 2, from 70 to 72, the water temperature of the heating medium, whatever they may 5 be, may have fluctuated as much as 100 or, in some instances, as in the case of hot air systems, even more. Many rate, by the time the room temperature has increased the 2, that is, to bring it up to 72, a considerable quantity of heat 10 has been transmitted to the heating medium, and this residual heat continues tobe dissipated into the room, even though the thermostat has already shut off the burner. This residual dissipation of heat continues to raise the temperature 15 of the room so that, actually, the temperature of the room may be increased to as much as 75 before this residual heat has been entirely dissipated and further heating of the room terminated. This condition is frequently termed over- 20 shooting or overrunning because of the tendency for additional quantities. of heat to be poured into the room even after the cessation of operation of the heating means.

Similar conditions exist at the other end of as the differential range. For example, as the room temperature falls from above 72 to 70 in the illustration assumed. by the time this occurs, and particularly by the time that the room temperature as registered by the thermostat reaches '70", thetemperature of the heating medium, by which heat is transmitted from the furnace or burner to the room, has decreased materially, in some cases to almost room temperature. Therefore, at the instant that the room thermoa stat reaches 70 and theburner is started, it is necessary for the burner or furnace to first raise the temperature of the heating medium from approximately room temperature to temperatures materially greater, depending upon the system, 40 before any heat is actually sent out into the room. In a hot water system, the required temperature increase may be as much as 180'. This increase does not, of course, occur instantly but takes an appreciable length of time, and hence a the room temperature may continue to fall below 10 and may thus swing downwardly to as low as 6 5' in some instances before any substantial quantity of heat isactually delivered into the room.

Accordingly. therefore. while the room thermostat is arranged to start the burner at I0? and shut the some off at 12- the actual temperature of the room may vary as widely as from to Such variations introduce imcomfortabie above.

conditions. A person in the room, say at 75, becomes accustomed to that temperature and when the temperature swings downwardly through 70 to 65 the person feels uncomfortably cold. Actually due to such variations a person may feel uncomfortably cold at 70.v Furthermore, due to the fact that the burner is shut oil at 70 and the temperature of the heating medium drops to approximately room temperature, appreciable time is required to raise the temperature of the heating medium and the air in the room may become stratifled, that is, certain portions of the room may be inuch below '70", even though the thermostat may be disposed in a layer of air having a temperature of 70 or This stratiflcation of the air is due. at least in part, to a lack of circulation, and the lack of circulation is due, at least partly, to the fact that there is no heat in the radiator and therefore it does not promote the circulation of the air. This condition is apt to be prevalent in warm air heating systems, as well as in steam, hot water, and other heating systems.

With these factors in mind, the principal object of the present invention is to maintain the temperature of the heating medium within relatively narrow limits during the normal operation of the heating plant, as by starting or stopp s. or otherwise increasing or decreasing the effectiveness of the operation of the burner independently of the room thermostat and even within the range of the temperature diflerential for which the thermostat is adjusted. By virtue of such means, a much more sensitive type of control is secured than hitherto possible. According to the present invention, however, the thermostat does not at any time lose control of the operation of the burner or other heating means.

Another object of the present invention is the provision of means for controlling heating systems whereby the ordinary thermostatic control is augmented'by a separate control which, while it does not displace or interfere with the thermostatic control, serves to maintain the room temperature within narrow limits at approximately the lower setting of the thermostat. Still further, another object oi the present invention is the provision of separate control means which serves to maintain the room temperature within narrow limits at approximately the higher thermostatv lhus, when the temperature of the medium is descending, if the control is so performed as to maintain the temperature of the room at nearly the upper or higher limit of the thermostat setting, the tendency for the temperature of the heating medium to w downwardly too far is eliminated, and, ly, where the control is effected-by the ascending temperature of the heating medium. the feature of holding the room temperature at a point adjacent the lower thermostat setting prevents the overshooting of the temperature of the heating medium.

It will be apparent, of course, that all of these factors contribute to the maintenance of substantially uniform temperatures in the room or other space to be heated.

A further object of the present invention is the provision of a combination control in which the higher heat requirements are met by an arrangement wherein the control generally operates on the descending principle and in which the lower heat requirements are met by the control generally operating only on the ascending principle.

Another object of the present invention is the provision of means for periodically modifying a room temperature responsive control according to fixed temperature increment or decrement of the heating medium by which heat is transferred from the heat source to the space to be heated. The use of a periodical control based on a fixed temperature change in the heating medium automatically adjusts the system for most emcient operation at the rate of heat dissipation under which the heating plant is operating.

An additional obiectofthe present invention is to control a heating system by an auxiliary control which throttles but does not cut off the heat source entirely or start the same up fully, whereby changes in the heat demand are, in effect, anticipated so that a more nearly uniform temperature is maintained at all times.

These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description of the preferred arrangements, taken in conjunction with the accomp nying drawings.

In the drawings:

Figure l is a diagrammatic view showing a heating piant'with a controlling room thermostat in connection with circuits and control devices embodying the principles of the present invention and acting to maintain the room temperature at or near the upper differential limit of theroom thermostat:

Figures 2 and 3 illustrate different positions of the room thermostat;

Figure 4 is a perspective view of the heating medium thermostat which is responsive to. the temperature of the heatim medium. as distinguished from the temperature in the room, and which is adapted to momentarily complete a circuit every time the temperature of the heating medium increases or decreases a given amount;

Figure 5 is a modified form of the present in vention in which the room temperature is maintained at or near the lower differential of the room thermostat:

Figure 8 illustrates the switch device used with the heating medium thermostat in the circuits when arranged as shown in Figure 5;

Figures 7 and 8 show the circuits and heating medium thermostat when arranged to operate on the ascending and descending principles in combination:

Figure 9 is another modification of the present invention and illustrates means for securing a throttled action of the heat source so long as the room temperature is within the diiferential limits of the room thermostat;

Figures 10 and 11 are other modifications showing the use of the present invention in circuits involving two-position controls: and

Figure 12 shows thecircuitofFigures 10 and 11 when equipped with a combined control.

1 is prevented, thereby There are a number of well known systems for controlling the operation of burners, gas or oil, stoker or other means employed in automatic heating plants for the proper thermostatic control of the furnace or other source of heat, and for illustrating the principles of the present invention I have adopted a construction embodying a hot water furnace l fired by a gas burner 2 and arranged to contain a heating medium, such as water, which is directed through a supply main 3 to the radiators l in the room or rooms to be heated. The cool water from the radiating system, represented by the radiators 4, is directed back to the heater I through a return pipe 5. The gas burner 2 is supplied by gas from a supply conduit 6 controlled by a gas valve 1 of any desired construction. Preferably, however, the gas valve I is arranged to be controlled by an electric circuit, and one well known type of gas valve which may be installed in the construction illustrated includes an electric motor which is arranged to open the valve controlling the supply of gas through a train of gears. The motor operates on the stall principle, that is, the motor opens the valve until the latter reaches its fully open position and then further movement of the valve stalling motor. The valve then remains open until the circuit to the motor is broken, at which time the valve is closed by given point and-arranged to a spring or the equivalent, the motor and the train of gears being driven back to closed position by such spring. Such gas valves are well known in the art and the details per se form no part of the present invention, Any form of valve may be used if desired, such as valves of the solenoid or magnetic type. Electrically controlled throttle valvesand regulators may also be used where desirable for reducing or increasing the gas flow without actually shutting off all flow, as will be referred to later;

Also, it is to be further understood that the present invention is not necessarily limited to a hot water heater but may be employed on any heating system in which a source of heatutilizing any form of fuel available is arranged to heat a medium which is adapted to be directed to the room or space to be heated in which some form of radiating system, utilizing the heat of said medium, is disposed. In such case, the device I represents any known form of means for controlling the heat source, and in case the furnace I is fired by a solid fuel, such as coal or the like, the device i represents any known device for controlling the damper or any mechanism by which the rate of feed, as by a stoker, is controlled.

One means for controlling the burner or heat source of an automatic heating system which has proven satisfactory in service is one in which the control device I is under the control of a thermostat located in the room or space to be heated and arranged to start the operation of the heating plant when the room temperature has fallen to a stop the operation when the temperature, of the room as registered by the thermostat has reached a second given point. Thus, the furnace, boiler or the like, is intermittently operated for such lengths of time that the radiating system acts to keep the temperature of the room orother space fairly constant. Preferably, however, the thermostat is arranged with a given temperature dlflerential,

that is, thethermostat closes certain contacts at one-temperature to start the burner and opens such ,contactstor other contacts at aaslightly higher temperature to stop the operation of the being known as the temperature diflerential of the thermostat and is desirable so that the temperature of of the temperature differential, without having the thermostat constantly making and breaking the connections, or the burner being constantly started and stopped at relatively short intervals.

As mentioned above, there is a considerable lag in the responsiveness of such a system. Between the time that the burner is started and the time that the temperature of, the room has been raised to a point that the thermostat moves to stop the operation of the burner, a considerable quantity of heat has been transferred into the heating system so that the temperature of the room tends to rise above the upper limit of the temperature differential of the thermostat, even after the burner or other heat source has been shut off or reduced. Similarly, after the burner has been shut oil the heating system cools down, so that there is a considerable lag between the time when the thermostat subsequently calls for more heat and the time when the room begins to be heated, for the burner must operate for some time in order to first raise the temperature of the heating medium from room temperature up to its effective heating temperature. The result. of this arrangement is that, actually, the temperature of the room falls to a considerable point below the lower limit of the differential of the thermostat before heat is sent up to the room, and likewise the temperature of the room rises above the upper differential limit before the heat is cut off.

In the drawings, the reference numeral it] indicates one type of thermostat which is in use at the present time and which embodies an ornamental casing Ii or the like in which is disposed at temperature responsive coil l2 carrying two contact blades l3 and II. These contact blades l3 and I4 are electrically connected together and to the thermostat coil l2 and are arranged to engage, respectively, contact points l5 and IS.

The thermostat is adjustable for securing various temperatures in the room or other space to be heated and, likewise, the temperature differential may be any desired quantity. The details of thethermostat itself form no part of the present invention, but for purposes of illustration the thermostat III is shown as arranged to control the furnace l with a temperature differential of approximately 2, and preferably the burner is started when the room temperature reaches 70 and is shut. off when the room temperature reaches 72", This may, of course, vary.

Figure 1 illustrates the relation between the contact blades l3 and M and associated contacts (Sand it when the temperature is above 72.

Figure 2 represents the position of the parts ,Figure 3. Preferably, the thermostatblade I3 is flexible to accommodate this operation.

Referring now to Figure 1, it will be observed that the gas valve 1, which represents any known means for controlling the starting and stopping or other means tor increasing anddecreasing the effectiveness of the heat source, is energized by theroom can vary within the range .conductors II and I! from the line L, the conductor it including a line switch 20. The line switch 20 is mechanically interconnected'with a holding switch 2|, as by being associated with the plunger of a relay coil 22 in any well known manner.

Connected across the line L is the primary 22 of a transformer 24, and one end oi the secondary 26 of the transformer is connected by a lead 26 with the relay coil 22. The other end of the relay coil 22 is connected by a lead 21 with thecontact l5, and the other end of the secondary 25, opposite the end towhich the conductor 28 is connected, is connected by means of a lead 2| with 5 the contact l5.

From the construction so far described, it will be observed that when the thermostat switch blades it and II have been moved to the position shown in Figure 3, corresponding to a room tem- 90 perature of 70 or lower, a circuit is established from one side of the secondary through the conductor 26, the relay coil 22, the contact I6, the switch blades I4 and IS, the contact l5, and back through the lead 2| to the other side of the sec- 25 ondary 25 of the transformer 24. This energizes the relay coil 22 and causes the same to pull up the switch 2|], thus closing the line circuit to the burner control device I and causing the same to open the valve so that gas will flow to the 30 burner 2, at the same time igniting the same by any suitable means well known in the art, such as by a pilot light. At the same time that the relay 22 pulls up the switch 20, the switch 2| is also closed. and the switch 2| is connected,

35 through a short lead 25, with the same end of the relay coil 22 to which the conductor 21 is connected. The contact engaged by the switch 2| when it is closed by the operation of the relay coil 22 is indicated by the reference numeral 36. 4n and this contact is connected by means of a conductor 21 with the thermostatic coil l2.

As a result of this construction, as long as the relay coil 22 is energized the line switch 20 is kept closed which; in turn, drives the motor of the gas valve into its stalled position and holds the motor in this position, thus maintaining the gas valve open until a time when the relay coil 22 is deenergized which then permits the switches 22 and 2| to open. However, as soon as the relay coil 22 is energized in the first place, the closing of the switch 2| serves to establish a circuit from one side of the relay coil 22 through the switch 2|, the conductor 21, the thermostatic coil l2, the thermostat blade It, the contact I5. and the conother end or the relay coil 22 is connected, as through the conductor 26. There is thus established a holding circuit which maintains the relay coil 22 energised, even though the thermostat should uncoil'to the extent 01' moving the thermostat blade ll away from contact it (the position shown in Figure 2), thus breaking the circuit at this point-but maintaining the relaycoil energizedbythecircuitthroughtheclosedswitch' both tblades l2 and II are separated iromthdrecntactsliandll. Asaoonasthe ductor II with the secondary 25 to which the connection is broken at Iii-l 5, the holding circuit through the conductor 21 is interrupted and the relay coil 22 is no longer energized. This permits both switches 20 and 2| to open, thus shutting oil the burner 2 and disconnecting the holding 5 circuit which maintained the relay 22 in energized relation after the connection has originally been interrupted at ll-l 8. Except by means which is to be described later and which forms a part of the present invention, 10"

current cannot be reestablished through the relay coil 22 by the means described above to start the burner again until the room has cooled down suiflcientl'y to cause the thermostat l2 to contract and to close both thermostat blades l3 and I4 against their respective contacts l5 and it, which in most installations is not attained until the temperature in the room as registered by the thermostat has fallen to 70. So far as the present invention is concerned, the means described above is old and well known and the details thereof per se do not form any part of the present invention except as an element in the novel combination. From the above description it will be apparent that the gas valve I will be opened to start the burner 2 whenever the temperature in the room drops to 70 to close the relay circuit through the engagement of the switch blades l3 and M and the respective contacts l5 and I6, and it will also be observed that the burner 2 is maintained in operation until the temperature in the room has reached 72 at which time the holding circuit through the conductor 31 is broken by the separation of the thermostat blade I2 from its contact I5. Maintaining the burner 35 in operation in this manner until the room thermostat registers a temperature of 72 tends to cause the overshooting or overrunning mentioned above, that is, the temperature of the heating medium in the burner l and the supplymain is raised to such a point that there is a considerable quantity of residual heat which continues to be transmitted into the radiating system 4 so that the temperature or the room continues to rise for a period of time to a point about 72, even though the burner has already been cut oil. Similarly, when the temperature in the room has fallen to 10, the point at which the burner 2 is started up, the temperature of the beating medium, by which heat is transferred from the thermostat to the rooms, may have fallen to almost room temperature. Thus, there is a period or time during which, even though the burner 2 is in operation, no heat is yet sent up to the rooms, and hence the temperature or the latter continues to fall below the lower limit, namely "10, 01 the temperature diflerential. In one form of the present invention, these undesirable swings or variations are eliminated by means which, when arranged as shown in Figure 1, op- 00 crates to start the burner 2 after the temperature in the room has dropped to 72, or alter the temperature tails to such a point that the thermostat coil l2 moves the contact l2 back into engagement with the contact Ii, even though the 05 blade ll has not been moved into engagementt with the contact IS, a necessity for starting up the burner according to the prior at One means which I have provided for starting up the burner when the temperature of the room hastallento'lTisshownlnFigure Land. in general, constitutes a'shunt circuit around the switch 2| and is operative, in series with the contact: "-42, to elosethe lineswltch 2| bymeans'. which is dependent upon two interrelated iac- 78 eral, a thermostat 45 l 50, the upper portion amass:

tors, namely room temperature and temperature of the heating medium itself. This means constitutes, with other modifications, the principal part of the present invention and includes a thermostat device indicated in its entirety by the reference character T which comprises, in gencontrolling a switch 50 which, through leads-5i and 52 connected. respectively, with the conductors 2i and 21, serves to temporarily short-circuit the switch 2i and, ifa connection is established at the contacts I! and IE, to thereby close or complete the circuit from the secondary of the transformer 24 through the relay coil 22, the lower portion of conductor 21, the leads 5| and 52 and the switch of the conductor 21, the thermostatic coil l2, the the conductor 3i. Since the contacts it and ii are not closed unless the room temperature is at or below 72 it will be noted that the closing of the switch 50 will have no eflect as far as energizing the relay 22 is concerned unless the connection is completed at l2, l5, but if these latter contacts are in engagement. then as soon as the room temperature drops to 72 and as soon as the temperature of the heating medium is such that the switch 50 connects the conductors 5| and 52, the relay 22 is energized without waiting for the room temperature to drop to '10", which would close the contacts H and 16, as would be necessary if the circuits were operated according to the prior art. a

The device T, illustrated somewhat diagrammatically in Figure 1, is shown more in detail in Figure 4 and includes a supporting plate or housing 50 to which one end of the thermostatic coil I5 is connected; The other end of the coil 45 is connected, as at 51, with a thermostat shaft 52 journaled for rocking movement in the housing iii, as is usual in this type of instrument. The outer end of the thermostat shaft 52 carries a notched segment 63 adjacent which is'pivotally mounted, as at 5|, a mercury switch tube which constitutes the principal movable portion of the temperature responsive switch 51' The electrodes 66 and 81 are disposed adjacent one another in the central portion of the mercury tube 55 and the conductors 5i and 52 are connected thereto so as to be closed by a globule of mercury 89 which is disposed within the mercury tube 55.

The notched segment 63 cooperates with an escapement member 1| carried by and movable with the mercury switch tube and has pallet portions 18 and I4 spaced, as indicated in Figure 4. so that as the segment or plate 63 is rocked under the action of the thermostat coil 45, the mercury tube 55 will be tilted back and forth about its axis 54 causing the mercury 69 to momentarly connect the contacts 56 and 81 every time that the temperature of the heating medum' changes enough to swing the plate 82 through half the distance between notches.

Obviously. other means may be provided fortilting the mercury tube '55 in accordance with temperature changes in the thermostat coil 45.

As indicated in Figure 1, the device '1 is placed on the upper part of the heater I with the thermostat col 45 disposed in thermal relation with the heating medium, either by being placed therein or by being disposed against the side of the heater, as in the case of contact thermostats. The device T may also be placed somewhere in the supply line 3 containing the heating medium by which the heat is transferred from the burner contacts l3 and i5, and I to the radiating system in the room or rooms. As the temperature of the heating medium changes, the notched segment 62 is swung in one direction or the other, and each time a notch passes one of the pallet portions II and 14 the mercury switch tube is swung from one position to another, and each time the mercury tube 85 is operated, the globule of mercury 69 passes the electrodes 86 and 51 and temporarily shortcircuits the same to energize the relay coil 22 if the room temperature is such that the contacts i3 and I5 are engaged.

For hot water heating systems, thesegment i3 is preferably arranged so that the electrodes 68 and 01 are electrically connected together momentarily for every fifteen degrees change, in the temperature of the heating medium, but obviously, of course, this thermal periodicity may be greater or less if desired and depends upon the particular type of heating system with which the present control means is associated. For example, in hot air heating systems, the period desired may be in the neighborhood of thirtyflve degrees, more or less.

The operation of the mechanism described above with the device T embodied in the circuits as indicated in Figure 1, is substantially as follows:

Assuming, first, that the temperature of the room has fallen to a point below the lower limit of the thermostat diflerential, which lower limit is generally, but not necessarily, in the neighborhoodof 70 F., the thermostat coil l2 will have swung the contacts l2 and II to the position shown in Figure 3, and this will have established a circuit from the secondary of the transformer 24 through the relay coil 22 as described above. thus closing the switches 20 and 2|, the switch 20 serving to open the gas valve I and start the burner 22. Now as the temperature of the heating medium increases, the medium will be caused to fiow through the radiating system 5 and heat the room, returning to the furnace I by way of the return pipe 5. As the temperature of the heating medium increases. the coil 45 will be actuated to rock the segment 52, swinging the mercury switch tube 65 from one side to the other at every fifteen degrees of increase, or approximately so, but this will have no eilect on the system because the initial operation of the relay coil 22 serves to close the switch 2| and maintain the relay coil 22 in energized relation so long as the connection at I! and I5 remains in engagement. However, as sooon as the room temperature exceeds the upper diflerential limit, 72 F. in the assumed setting, the connection is broken at It and I5 and the relay coil 22 is deenergized, thus interrupting the connections to the gas valve 1 and allowing the same to shut off the gas supply to the burner 2. Although the burner is now shut 01!, there is a quantity of residual heat in the system so that the temperature of the room may, for a time, remain above the upper differential limit '72. However, as soon as the burner 2 is shut oil. the temperature of the heating medium falls, and, likewise, the segment 63 will now be swung in the opposite direction under the action of the coolin on o! the thermostat coil 45 disposed in thermal relation with respect to the heating medium. as indicated in Figure 1. For every fifteen degrees during the lowering of the temperature of the heating medium, the mercury globule 69 will temporarily short across the electrodes 55 and 51, but so long as the room temperature is still above the difl'erential limit of the thermostat, namely, 72, there will be no electric circuit completed through the relay coil 22, and therefore the burner will not come on. However, when the room temperature has descended to 72, or slightly lower, the contacts I! and I! will be in engagement, and as soon as the temperature of the heating medium has cooled suflicient to once more operate the mercury tube 68 the shorting of the electrodes 66 and 61 by the mercury globule 69 will serve to connect the conductors ii and 52 and a circuit will at once be completed from the secondary of the transformer 24 through the relay coil 22, the lower portion of conductor 21, the conductors Ii and 52, the thermostat contacts i3 and I5, and the lead Ii. The burner will therefore be brought into operation again and will then remain in operation until the room temperature has reached the upper diflerential range of the thermostat and will again be shut down by the separation of the contacts II and i5, until the cooling oi the heating medium, actuating the thermostat l5, and the cooling of the room temperature down to"l2 will again establish a circuit through the relay coil 22 and again bring the burner into operation.

From the above described operation, it will be noted that as the temperature of the heating medium decreases, the electrodes 68 and 61 will be closed at definite intervals, and if the room temperature has decreased even slightly from the upper diflerential range of the thermostat, namely, 72 under the conditions assumed, the burnerwill come on and will bring the room temperature back to this setting before the burner will again be shut oil. The result of this arrangement is to prevent the extreme swings in the temperature of the heating medium which commonly follow the operation of a control arrangement wherein the temperature of the room must descend to the lower diflerential limit before the burner can again be brought into operation. With the control performed according to the principles of the present invention, there will be less stratiflcation of the air, partly because of the maintenance of some circulation by preventing the heating medium from becoming. cold, and also there will be a more constant temperature 'in the room and a more comfortable general heating condition. As will be obvious, the above described system tends to keep the temperature of the room at or near the upper diiferential limit of the thermostat and is operative principally during periods of descending temperatures of the room and or the heating medium. The above described arrangement may therefore be designated as an application of the principles of the present invention to descending temperatures.

To utilize the principlesof the present invention by applying the same to the control of the burner on ascending temperatures, substantially the only change required in the circuits shown in Figure 1 is to arrange the device T in series with the holding switch 2|, instead of in parallel as shown in Figure Land to arrange the mercury switch tube 85 so that the circuit through the associated leads is momentarily broken, instead of being momentarily established as indicated in Figures land 4. Figure 6 illustrates the mercury switch tube of the second thermostat device T arranged for utilization in a circuit operating on the principles of ascending temperatures, and it will be observed that, instead of having two electrodes in the central portion of the mercury switch tube 85, two pairs of electrodes are utilized, two electrodes being at each end of the tube. The reference numerals 80 and ill indicate one pair of electrodes at one end of the tube, and the reference numerals 82 and 83 indicate the other pair of electrodes.

Figure 5 shows a form of circuit which may be employed when my control means is arranged for ascending temperatures. The electrodes 80 and 83 are electrically connected together and to a conductor 85, and the other electrodes, BI and B2, are also electrically connected together and to a conductor 86. Referring now to Figure 5 in which the circuit for this arrangement has been indicated, it will be observed that the contact 36, which is adapted to be engaged by the switch 2| when the latter is closed by the energization of the relay coil 22, is connected, not with the conductor ill as indicated in Figure 1, but with the conductor 86 leading to one set of the electrodes, ill and 82. In Figure 5 the lower portion of the conductor 31, which is connected with the thermostat coil i2 and which, in Figure l, was connected with the contact, is now connected in Figure 5 with the conductor 85. This arrangement disposes the thermostat device T in series with the holding switch 2|. The other circuits are the same as indicated in Figure 1 and the operation of the circuits shown in Figure 5 is substantially as follows.

When under the conditions assumed above, the temperature of the room is above 72, or below 70, that is, outside the temperature difierential range of the thermostat ill, the burner is started or stopped by the action of the thermostat ill in the usual manner and the making or breaking of the connection between conductors 85 and 86 has no eiiect whatsoever. That is to say, if the temperature is below 70, the relay coil 22 is energized by the closing of the contacts l4 and I6 and the contacts l3 and I5, and if the temperature is above 72, the upper differential limit, the

relay coil 22 is not energized because the connection is broken at the contacts i3 and it, regardless of the position of'the thermostat device T.

Assuming, now, that the burner was started by the temperature of the room falling below 70 closing the contacts l3-i5 and 14-46, and has operated sufliciently to bring the temperature of the room to a point within the diiferential range of the thermostat III, that is, between 70 and 72, the contacts II and It will be in engagement but the contacts I and I6 will not be engaged. Normally, however, the relay coil 22 will remain energized by a. completion of the circuit from the secondary oi the transformer 25 through contacts I3 and I5 and either the contacts 80 and II or the contacts U2 and 83 of the second thermostat T and through the switch 2i which was closed by the initial energization of the relay coil 22. However, as the burner is maintained in operation and the temperature of the heating medium increases, the thermostat device T will operate to momentarily break the connection between the conductors 85 and N, by swinging the mercury switch tube from one side to another and by thus causing the mercury globule to leave the two electrodes which it had previously served to connect. The purpose of momentarily breaking the circuit at this point is to shut down the burner if the room temperature has increased to some 'point adjacent or slightly above the lower diflerential limit of the thermostat so that the contacts i4 and it are separated, for the contacts 01 the device T and the switch 2| are masses in series and the moment the contacts II and ii are separated, the relay coil 22 is deenergized and the switch 2| immediately opened. Since the switch ii is then opened the subsequent connection oi the other pair of contacts in the mercury switch tube as the latter completes its swing, will have no effect. Therefore, the burner will be shut down and will stay shut down until the temperature of the room has dropped to or below the lower temperature diflerential oi the thermostat, namely at which time the thermostat I! will then cause the contact it to engage the contact l6 and therefore will establish a circuit through the relay coil 22 in the usual manner. This will then close the switches 28 and 2| and the burner will stay on until the contacts II and i6 separate and the rising temperature of the heating medium causes the second thermostate device T to momentarily break the connection between the conductors B5 and 88, whereupon the burner will again be shut down until the temperature in the room falls to the lower differential limit.

The action of this method is, thereiore, the reverse of the arrangement previously described above in that, where before the tendency for the arrangement was to cause the room temperature to be maintained at the-upper differential limit, the present arrangement is such that the tendency is to maintain the temperature of the room at the lower difi'erential limit. This is accomplished by preventing the temperature of the heating medium from rising above the temperature that is necessary or the heating requirement, for as soon as the room temperature is brought up to the lower differential limit, a slight increase in the temperature of the heating medium, an increase of 15 where the heating medium is water under the conditions assumed, will cause the burner to be shut off.

One of the advantages of the ascending principle is that the system is not disturbed by jars, such as those caused by passing street cars. a person walking across the room, etc., or by sudden changes oil temperature, as by'opening a door, which under the descending principle may cause the burner to be shut ofl at short intervals. 0n the other hand, under the ascending principle the room temperature is maintained at approximately '10 degrees, the lower diflerential limit,

and this keeps the switch blade IS in firm engagement with the contact 15, for even when the blade H is just about to leave the contact It, the blade I3 is still under appreciable tension acting to hold it more or less firmly against the contact l5 (see Figure 3). Therefore, irrespective of whether or not the thermostat blade l4 momentarily leaves its contact 16, as by being jarred, the burner is maintained in operation and jarring will not affect the same because of the biased condition of the switch blade l3 and the mercury connection at the device T (Figure 5) between the conductors 85 and 86. However, at

every thermal period (15 as assumed above) the device T serves to break the circuit unless the switch blade 14 is already out of engagement with the contact 16, so that whatever fluttering or jarring there mayoccur will have no effect unless exactly at the moment that the mercury is moving from one end to the mercury tube to the other, but as is obvious, this is not likely to occur at all and, at most, can continue for only a very small fraction of time and, hence, can be ignored.

Another advantage of the ascending principle is that at the higher heat demands the burner is kept on for longer periods oi time, because. to raise the water temperature the fixed amount, 15 as assumed, requires much more time when the water temperature is relatively high to begin with than when the water temperature is lower. There may actually be times when the furnace is operated near its maximum and the water temperature does not change as much as 15. Where the time interval between the 15 changes is thus increased, the tendency is to maintain the room temperature at a greater average than obtains when the weather is milder and the water temperature is somewhat lower. Accordingly, therefore, a system constructed according to the principles of the present invention operates at certain thermal periods, depending upon fixed temperature changes in the heating medium, to automatically readjust itseli' to efiiciently accommodate the demands to which it lssubjected.

From the above description of the two arrangements. it becomes apparent that each has its. advantages and that, in each arrangement, there is provided two thermostats, one responsive to the temperature of the room for starting up the burner when the room temperature tails below a certain temperature and for shutting oil the burner when the room temperature exceeds a given temperature, regardless of the condition of the second thermostat.

It is also observed that in both cases the second thermostat T is. first, operative only when the room temperature is within the temperature differential of the thermostat setting and, second, it is responsive to the temperature oi the heating medium and controls the burner circuits in such a manner that the room temperature is kept practically constant and does not swing upwardly or downwardly appreciably above or below the temperature diiierential of the thermostat. Nevertheless, the room thermostat is at all times maintained in normal control of the burner, for

in any position of the device T the burner is shut of! when both switch blades l8 and il are open and the burner is started up when both blades i3 and I4 engage the contacts l5 and I8.

Reference is made above to the fact that the arrangement shown in Figure 1 is such that as the temperatures descend, the room temperature is prevented from swinging downwardly too far by starting up the burner just as soon as the descending temperature of the room reaches the upper thermostat difierential, and in the second arrangement described above it was set forth that during periods of ascending temperatures, the temperature or the room was prevented from overrunning or swinging upwardly too far by shutting oi! the burner just as soon as the room temperature had been brought up to the lower differential limit. These two principles of operation are particularly adapted to be-combined in a single control arrangement and is especially eiiicacious in preventing large temperature overruns or excessive temperature lags for it, as the temperature of the heating medium tends to swing downwardly, the burner is started up at the upper differential limit and as the temperature tends to swing upwardly the burner is shut as at the lower differential limit, the net result is that as long as the room temperature is substantially within the differential limits of the room thermostat the temperature of the heating means remains about the same and, i

eifect, the heating plant control floats between the two systems.

One arrangement for combining both the ascending and descending principles in the same system is shown in Figures 7 and 8 which illustrate means tending to prevent the temperature of the heating medium from exceeding that to bring the temperature of the room up to the proper point and, at the same time, is operative to turn the burner on, even when the temperature of the room is within the diflerential range of the thermostat in order to prevent the room temperature from falling too low so as to be carried below the lower differential limit before the burner can be started up and made effective to send up heat to the room.

One means for accomplishing this result takes the form of a construction wherein a mercury switch tube embodies the connections shown in Figure 4 and, in addition, the connections shown in Figure 6, together with a changeover switch blade irictlonally associated with the plate 82 and moved, in accordance with temperature changes in the heating medium, from one position to another, one position cutting in circuits so that the thermostat device I. is arranged in serieswith respect to the holding switch 2i, as shown in Figure 5, and the other position cutting in circuits to arrange the thermostat device I for operation in parallel with respect to the holding switch 2|, as shown in Figure 1. A thermostat device built along these principles is illustrated in Figure 8 in which the shaft 62 oi. the thermostat coil 45 carries the plate 62 and tact m with which stationary contacts 402 s e Preferably. such contacts electrodes ll and I2 is connected to the lower llo. oi the conductor 21 leading to the lioitheholdingswitchlLasbesi-shown 7w issimilartol 'lguresiandli tes the circuits involved. As also showninl'igures'landitthechangeover blade contact III is connected by means I" to the upper portion of the whichis connected with the ther- 8 will be observed that the tch blade Ill frictionally engages the thermostat shalt I2, and hence whenever ggnog Plateilisswunginonedirectiomasbyan ascending temperature of theheating medium. the contact III is swung in the same direction until it engages one of the contacts I02 and ill,

and when the plate I is swung in the other direction. as by a d temperature ota the temperature or the heating medium has swims the plate 63 to a-position to cause the contact in to engage the contact In, the operation r the circuits is-the same as for the circuits shown in Figure 5. That is, assuming that the room temperature had previously fallen to below 70 so that the relay coil 22 was energized by closing the circuit at contacts l5 and I, then the holding circuit for maintaining the switches and 21 closed, even after the room temperature has exceeded 70 and the contacts at It opened, is completed as follows from the secondary oi the transformer 24 through conductor ll, contacts l5 and i3, thermostat coil l2, the upper portion of conductor 31, conductor i01, changeover switch blade contact ifll, contact I02, lead I08, the globule of mercury in one end 01' the switch tube 65a, conductor 86, the lower portion Ila of conductor 31, contact 38, switch 2i, relay coil 22, and conductor 26, back to the secondary 25 of the transformer 2|. However, as the burner 2 is maintained in operation by the relay coil 22 holding the line switch 20 closed and as 'the temperature of the heating medium ascends, the swinging movement of the notched plate '2 will cause the mercury switch tube 654 to swing in a clockwise direction, as viewed in Figures '1 and 8, thus interrupting the holding circuit through the relay coil 22 when the globule oi mercury leaves'the left hand end 01' the tube and the electrodes III and Ii connected by the globule in that position. This will cause the relay coil 22 to be deenergized, thus opening the switches 20 and 2i, unless, of course, the room temperature is 70 or less and the contacts I and ii are in engagement. It the room temperature is above 70", the burner 2 will not come on again until the room temperature coasts down to 70 and the contacts II and it closed. When this does occur the relay coil 22 is energized in' the usual way. Thus, during ascending temperatures the arrangement shown in Figure 8 serves to tend to hold the room temperatures at the lower differential so as to prevent overrunning in the upward direction.

It will be observed, however, that under the conditions just assumed. as the globule of mercury shifts from the left hand end of the mercury switch tube a to the right hand end thereof, the holding circuit, while momentarily broken, is immediately reestablished by the globule of mercury connecting the two electrodes at that end or the tube. However, this does not energize the relay coil 22 because the momentary interruption has already caused the switches 20 and 2i to open, and since 'the switch 2! is then open. the circuit cannot be completed, even though the two electrodes at the right hand end oi the mercury switch tube are connected by the mercury globule 69. As the temperature of the heating medium continues to rise, every 15, or whatever the thermal period chosen may be, the mercury switch tube a will be oscillated, momentarily interrupting the connection between the upper and lower portions of the conductor 31 through the thermostat device '1', but unless the room temperature has dropped to after the circuit is once interrupted and has started the burner 2 and closed the switch 2|,

no eflect will be produced until the room temperature actually reaches the lower limit of the temperature diilerential.

When the conditions are such that the room temperature is above '12 and the burner 2 has been turned oil or the operation of the heatin means otherwise reduced, the temperature of the heating medium begins to fall, and in this case the thermostat plate I! will be" swung in the opposite direction. namely. in a clockwise directionasviewedinl'lgure8. 'I'heinitiai movement of the plate "in this direction will 'ilrst separate the contacts IOI and I02 and engage the contact IOI with the contact I00, thus arrangin the circuits for operation in a mannot similar to that set forth in connection with figure 1, namely, for descending temperatures. In this case, then, the contact III will be in the position shown in dotted lines in Figure 'l with the result that the shunt circuit around the holding switch 2| is normally open because the globule of mercury remains at one end or the other of the mercury switch tube. However, as soon as the room temperature descends to the lower diflerential limit, namely 70, the relay coil is energized in the usual manner, through conductor 2|, contacts I and I6, conductor 2], relay coil 22, and conductor 26. The energlzation oi. the relay coil 22 immediately closes the line switch 20 and the holding switch 2|, and now a holding circuit is established to maintain the relay coil 22 energized and the switches 20 and 2I closed. This circuit is as follows: From the secondary of the transformer 24 through conductor 20, relay coil 22, lead 25, switch 2|, the lower portion 31a of conductor I 21, conductor 86, contact I03, changeover switch blade contact IOI, conductor I01, conductor 31, thermostat coil I2, contacts I3 and I5, and conductor 2|, back to the secondary of the transformer. The moment, however, that the room temperature is increased to the upper differential limit, namely 72, this holding circuit is broken at the contacts I3 and I5 and the relay 22 deenergized. However, as the temperature of the heating medium descends, the switch tube 65a will be oscillated every and at each oscillation the mercury globule within the tube will momentarily connect the electrodes 00 and 61. If the room temperature has fallen to 72, the relay coil 22 will be energized, even though the switch 2I is open, by a circuit through conductor 26, relay coil 22, the lower portion of conductor 21, lead ii, the globule of mercury within the switch tube as it passes from one end to the other.'the other lead 02, the lower conductor 210, the lead Iiflcontact I02, the changeover switch blade contact III, the conductor I01, the upper portion of the conductor 21, the thermostat coil I2, the engaged contacts I3 and I5,

, and the conductor 3|. Thus, as the temperature of the heating medium descends, the burner is placed in operation the moment the room tempuenrfiture has descended to the upper differential In the above mentioned arrangement, it will be observed that I have embodied in one system the two systems shown separately in Figures 1 and 5, respectively. Each system is controlled so as to be brought into operation during the' portion of the cycle in which its use is of the greatest advantage, and in actual operation the normal condition is that e controlmechanism floats between the two-systems, that is, the temperature is accurately maintained between relatively narrow limits, but should either of the limits be exceeded for any reason, in one direction or the other, the control mechanism be comes active to bring the temperature up or down toward the other limit, thus immediately and automatically eliminating further fluctuations.

In the arrangements described above and embodying the principles or the present invention, temperature fluctuations were eliminat d rethermostat,

duced by means which operated to keep the temperature at or near either the upper diflerential limit or the lower diil'erential limit, or by means utilizing a combination of such limit controls. The present invention also contemplates means for reducim or eliminating temperature fluctuations which is operative, as in the above modifications, only when the room temperature lies within the temperature differential of the room thermostat and is adapted, when the room temperature lies within this range, to throttle the operation of the heat source. That is to say, where the room thermostat is set to start up the heat source or otherwise increase the eil'ectiveness thereof at one temperature and to stop the heat source or otherwise decrease the eii'ectiveness thereof at another temperature, the present invention as embodied in the modification now to he described contemplates modifying this starting and stopping of the heat source or the increase and decrease In the effectiveness thereof, by operating the heat source in such a manner or at such a rate that its operation may be designated as lying intermediate the above mentioned starting up and shutting down or the increase and decrease in the effectiveness thereof.

As in the modifications previously described. in order to best show the relations involved in this form of my invention, I have chosen a hot water heater fired by a gas burner, the flow of gas being controlled in the first instance by a main gas valve opened and closed by electrical means. In Figure 9, however, I have embodied a slight addition. This addition comprises a device V embodying, first, a restriction in'the form of an orifice plate I incorporated in the gas supply main I2I leading from the gas valve 1 to the furnace I. Around the orifice plate I20 is arranged a by-pass line I24 in which is dis posed an electrically controlled gas valve I of any known construction and operating to open and close the by-pass line I24.

So far as the operation of the structure just referred to is concerned, these parts operate as follows. Whenthe main gas valve 1 is opened to receive a flow from the gas supply main 0, the gas reaches the burner through the line m and the orifice plate I20, and .also through the by-pass line I24, providing the gas valve I25 is opened. When this valve is openedthe furnace burner 2 receives the full gas flow, but if the valve I25 should be shut oil, then the only flow reaching the gas burner 2 is that passing through the orifice plate I20. Under this condition, hereinafter referred to as a throttled flow, the furnace operates at a reduced heat.

According to the principles of the present invention, the lay-pass gas valve I25 is controlled so as to be closed when the room temperature lies within the temperature differential of the room namely, between '10 and 12 under the conditions assumed for the modifications previously described.

The means so con olling the gas valve I25 comprises the following. In the circuit including the rocmthermostat coil I2 and the con-- ductor 31 there is embodied a relay coil I20 operating in conjunction with a plunger ISI which is connected with .a switch I22 similar to the line switches 20 and 2| referred to above. In addition to the'transformer 20, the line L is also provided with another transformer I24 which includes a primary I" connected across the line L and a secondary I20 one end of which is connected by a conductor I 31 with the electrically controlled valve I23 while the other end is connected through a conductor I30 with one end of the switch I32. If desired, however, the transformer I34 may be incorporated in or form a part oi. the transformer 24. A conductor I40 extends from the othertterminal of the electrically controlled gas valve I25 to a contact point III closed and opened by the switch blade I32 which, it will be remembered, is under the control of the relay coil I30.

Whenever current flows through the-relay coil I33, the switch I32 is closed, thereby completing the circuit through the secondary oi the transformer I as iollows: from the switch I32 through the conductor I33 to one end of the secondary I36, and from the other end of the secondary I36 through the conductor I37, the electrically controlled gas valve I25 and the conductor I30 back to the contact Ill engaged by the switch 'blade I32 when the relay coil I30 is energized. when current flows through this circuit the gas valve I25 is operated to close the by-pass line I23 so that gas admitted from the supply main 0 by the open gas valve I flows only through the throttled restriction I20. However, when the relay coil I30 is notenergized the switch I32 is opened and the gas valve I 25 is likewise open.

The circuits just described and'illustrated in Figure 9 have been embodied in the control circuit similar to the one illustrated in Figure 1, which showsa room thermostat I0 operating, through a relay 22, to control the "on" and "06 position of the main gas valve I in such a way that whenever the room thermostat I0 closes the circuit through the relay coil 22 by engaging the switch blades I3 and It with their contacts I5 and IS, the line switch 20 is closed and this opens the main gas valve I. As will be explained below and as indicated in Figure 9, a device T may be incorporated with the reduced fuel flow control, if desired, or it may be omitted. Assuming, first, that the device T is omitted in Figure 9, when both switch blades I3 and I4 ensasetheir contacts I5 and I6, the room temperature as registered by the thermostat I0 is below 70", under the conditions assumed. When the temperature of the room reaches 70 or slightly above, the connection at Il-It is broken, but the relay 2 continues to be energized by a holding circuit that comprises the following: the conductor 3|, contact I5, switch blade I3, thermostat coil I2, conductor 31, a direct connection across the conductors I01 and 06, switch 2I, lead 35, relay and 22, lead 26 and the secondary of transformer 24 back to the conductor II. In this way, the continued energization of the relay 'coil 22 continues to hold the line switch 20 closed and thusto maintain the gas valve I open. This circuit through leads and conductors including conductors 3| and 31, is thus maintained closed so long as the switch blade I3 oi the room thermostat ll remains in engagement with the con-' tact Ii, but under the conditions assumed, the

room thermostat I3 is arranged to separate these contacts when the mom temperature as registered by the room thermostatleaches 72, at which point the contacts are separated and the relay 22 deenergized, thus permitting the main as valve 1 to close.

A characteristic feature of the above mentioned control, which I utilize in the modification 01' my invention illustrated in Figure 9, lies in the fact that whenever the room temperature is below 70 or above 72 no current flows through conductor 3I,'but current does flow through this conductor whenever the room temperature lies between 70 and 72 due to the fact that in this temperature range, the relay coil 22 is held energized by the flow of current through the holding switch 2|, the conductor 31. the thermostat coil I2, contacts I3 and It, and the conductor 3|. Accordingly, therefore, I propose to make use 0! this characteristic feature by embodying my auxiliary relay coil I30 in the conductor 31, and such is the construction illustrated in Figure 9. In operation, therei'ore, as soon as the room temperature exceeds 70" and the contacts II and I8 separate, the conductor 31 carries the holding current, and the flow 01 this current through the relay I30 closes the switch I32 and energizes the lay-pass gas valve I25 to close the by-pass line I24 thereby throttling the flow of gas to the boiler I.

This is at once a simple and inexpensive yet eflicient means for reducing temperature fluctuations. In the embodiment chosen to illustrate this feature, as long as the room temperature is below 70 the burner 2 is maintained in its full on position, but as soon as the room temperature reaches 70 the burner 2 is throttied by reducing the gas flow thereto, and this reduced heat is maintained until the room temperature as registered by the thermostat I0 reaches 72, and then at this point the burner is shut ofl' entirely. In this form, as well as in the forms of the invention previously described, it will be observed that the room thermostat I0 retains its normal control of the burner at all times. That is to say, when the room temperature is below 70, the burner is turned on full, and when the temperature is above 7'2" the burner is shut ofl entirely. My invention is, of course,

not necessarily limited to a hot water heater or theme oi gas as a fuel, I br example, oil burn,- ers may be utilized, or stokers, dampers or other control means, may be actuated by the circuits shown in Figure 9, and such means need not necessarily be entirely shut oil at 72 or turned on full at 70, the only requirement being that the device I25 be utilized to secure a control position intermediate the control positions normally eflected by the room thermostat I0 at 70 and 72 room temperature. I

It will also be noted from Figure 9 that in the circuits there shown I also contemplate the use of the device 'I referred to above although such is not essential to this feature of my invention. Referring for the moment to Figure 1, it will be remembered that, with the device T embodied in the otherwise conventional circuits associated with the room thermostat I0, whenever the temperature of the room has been above 72 and is descending, as soon as a temperature of 72 "is reached and the temperature of the heating medium changes suiiiciently to actuate the device T and oscillates the mercury switch tube 50, momentarily connecting the contacts associated with the conductors II and 32, the relay 22 is energized by a flow of current from the secondcry of the transformer 23 to the conductor 3|, the contact II, the switch blade I 3, the thermostat coil I 2, the conductor 31, conductors l2 and ii, the lower rtion of conductor 21, to the relay coil 22. ow in Figure 9, the same arrangement obt with the exception that the momentary flowot current through the conductor 31 also energized the relay I30 to pull up the switch I32. In order to most conveniently amass:

illustrate this arrangement, as well as the one shown in Figure 5, which will be referred to later. I have shown in Figure 9 the thermostat device 'I 01' Figures '7 and 8 (which includes the features of both Figures 1 and 5) as connected in the leads 21 and 31 in the same manner as the device is connected in Figures l and 5. Just as in the case 01' the arrangement shown in Figure 1, in Figure 9 for every 15 change in the temperature oi the heating medium the contacts associated with the conductors 52 and ii are closed momentarily as the mercury flows from one end of the tube 65a to another but as soon as the relay 22 is energized, even though momen tarily, the switch 2i is closed, and thus the circuit .through the conductor 81 is maintained through the lower portion of the conductor 01, contacts IM and I03, since the temperature of the heating medium'is descending, and the switch 2|. although the conductors 02 and SI no longer carry current. Thus, although to secure the advantages referred to in the previous paragraph it is not essential to embody the device T, yet when this device is used the control of the heat source is more accurate because, after the room temperature has been above 72 and has descended to 72? so as to engage the switch blade IS with the contact I5, the device '1 responsive to changes in the temperature of the heating medium in the boiler I, temporarily closes circuits to start up the burner, thus tending to maintain the room temperature at or very near the upper dlflerentlal limit. However, where in Figure l the burner is started up full at 72, in Figure 9 the burner is started up at a reduced rate, by virtue of the energization of the relay coil I30 serving to shut oil the flow of gas through the by-pass I24 by closing the gas valve at an intermediate rate is an important feature in that it may require only a relatively small amount of heat to maintain the room temperature at 12. 01 course, if this reduced heat is not suiilcient to lreep the room temperature at 72, the upper diflerential' limit in thisinstance. the temperature of the room will iallto 70 or below, but as soon as 70 is reached the switch blade II will engage the contact I0, and this will so reduce the flow through the relay coil I20 will no longer be sumclent to pullup the switch I22. The latter will then p n and thus be energized by the gas valve control means I25 thereby opening the by-pass line I20 to permit a greater flow of gas to the burner 2. Thus, the burner 2 will be operated at its full $5 "on" position until the lower diflerential limit is reached or exceeded, and then the burner will he reduced because then the flow oi holding current through the conductor 31 will be sumclent to pull up the switch I22 and close the by-pass gas to valve I20 to again reduce the flow of gas to the burner. The flow 01' gas is, of course, not fully shut oil! to the burner, because there is a throttled now through the restriction I20, and this now may be sumcient at this time to maintain the i5 room temperature within the differential limit 7042", and ii the room temperature reaches or exceeds '12", its contact ll, thus cutting oil the entire flow of gas by the deenergization oi the main gas supply 10 valve 1. Then as the temperature of the heating medium descends and the room temperature coasts down to 72, the burner is again started up, but at a reduced rate, as described-above, and the above cycle of operation is resumed. :5 The throttling circuit, including the by-pass I20. Operating the burner the conductor 21 that the switch blade I2 separates tromcontrol valve I25, is also adapted to be installed in the arrangement shown in Figure 5. Figure 5, it will be remembered, shows illustrative circuits by which after the room temperature ilig rate, when the room temperature. reaches 70 ,of the notched plate vierential limits ofthe room ciflcally, during periods when the temperature reaches the lower diilerential limit, namely, 70', the device T, responsive to a change in the temperature or the heating medium, periodically opens the holding circuit through the conductor 31 to maintain the room temperature at or near the lower difierential limit of '10". The device T of Figures '1 and 8 when connected as shown in Figure 9 illustrates this arrangement and on ascending temperatures functions exactly like the arrangement shown in Figure 5, except that during the times that the holding switch 2I is maintained in closed position by the flow of holding current through the switch blade I3 and contact I! and the conductor 31 and the mercury in the switch tube of the device '1, the burner will be operated at reduced heat, since the current through the conductor 01 will energize the throttllng relay I20 to close the by-pass valve I25. For example, after for some time and the temperature of the heatmedium has fallen so that the. room. temperature swings down to 70, the burner will be restarted at full heat and the temperature of the heating medium will ascend. This will swing the arm I out of engagement with the contact I02 and over into engagement with the contact I02 (dotted lines in Figure 9 and full lines in Figure 8), but as soon as the room temperature exceeds '10 contacts II and III will be separated and the flow of current energizing the coil 22 will be diverted from conductor 21 to switch blade I0, conductor 01, coil I20, lead I01, contact IOI, contact I02, lead I00, the mercury in the tube 65a. conductor 08, switch 2| and back to the coil 22. The flow of current through the coil I30 keeps the switch I32, and hence the throttling valve I25, closed. However, as the temperature of the heating medium continues to rise, the movement 02 will oscillate the tube a and as the mercury runs from one end to the other the circuit through the coil 22 is broken and the holding switch immediately moves into its open position (Figure 9) and shuts on? the burner.

Thus, according to the principles or the present invention. I have provided means, operative in either or the modifications shown in Figures 1 and 5, for operating the source of heat at a reduced rate'whenever the temperature of the room lies within or between the upper and lower ditthermostat I0. 8118- o! the heating medium is descending. the burner is not started up at full operation, as in the arrangement of Figure 1, but only at a reduced temperature reaches 72 but lies above 70, and when the temperature of the heating medium is ascending, the burner is not shut of! completely, as in the arrangement of Figure 5, but only partially, when the room but is not above 72. It is to be noted that in Figure 9 the device T, as well as the by-pass control means V including the valve I25, are each arranged to be operated only when the temperature or the room lies between the upper and lower diflerential limits, but when the room temperature lies above or below these limits, the room thermostat resumes its normal and conventional control.

In all'o! the modifications described above, the conventional control circuits associated with the the burner has been shut oil a boiler I or other source of heat have included what I have termed a holding circuit or its equivalent, this holding circuit serving to establish the temperature differential between the limits of which my control means have been made operative. It is to be understood, however, that the principles of my invention are in nowise limited to association with such controls. For example, many controls in use at the present time embody a unit movable to either of two positions, depending upon whether or not heat is required. For example, the member controlled may be a damper, a valve, or any other means serving to start up or shut oil the fire or otherwise increase or decrease the effectiveness of theheat source. In Figure 10 I have shown a somewhat conventional means under the control of a room thermostat having a temperature differential, which has been assumed to be two degrees, namely, '10" to 72, to correspond with the conditions assumed for the previous modifications.

Referring now to FigurelO, the reference numeral I88 indicates, for purposes of illustration,

a gas valve having an operating arm I8I movable from an "oil' position to an "on position to shut off all supply of gas to the heater I, gas being supplied to the valve I88 by the main 8, as previously described. The room thermostat is of somewhat simplified construction as compared with the room thermostat I8 referred to above, and in Figure 10 the room thermostat is indicated by the reference numeral I83 and embodies a temperature responsive coll I84 and a switch blade or contact arm I88 adapted to engage adlustable contacts I88 and I81. The inner end of the temperature responsive coil I8! is an-' chored, as at I88, and is connected through a conductor I8I to one side of the secondary of the transformer II. I

A double relay I88 is provided and includes a,

pair of coils I88 and I81 in which is disposed a pair of piunsers or cores I18 and "I connected 7 together by a bar I12 the lower end of which is operatively connected, as at I18, with the end of the valve operating arm III. The coils I88 and I81 are arranged to cooperate with the cores I18 and I1 I, respectively, so as to shift the valve operating arm "I in one direction or the other, depending upon which one of the relay coils I88 and I81 is energized. The adjacent ends of the coils I88 and I81 are connected. respectively, with a pair of contacts I18 and I18 which are adapted to be engaged by a switch contact arm I11 connected, by a lost motion connection if necessary, to be operated by the bar I12 and anchored, as at I18, to a fixed pivot. The switch arm I11 is connected at I18 with a conductor I88 which leads to the end of the secondary of the transformer 28 opposite the end to which the conductor I8I is connected. The opposite ends of the relay coils I88 and I81 are connected, respectively, with the thermostat contacts I88 and I81, conductors I82 and I88 being provided for this P rpose.

Suitable snap mechanism is associated with the shiftable plungers I18 and I1I,and this mechanism may take any convenient form. For purposes of illustration, I have shown the upper end I88 of the relay coil cores connected to a pair of outwardly diverging links .I8I and I82, the outer ends of which are connected together by aspring I88. 'I'he outer ends of the links III and I82 are constrained for lateral movement only by suitable guides I88 and I81. By virtue of this construction, the links IIII and I8! serve as a toggle to interpose resistance to the initial shifting movement of the relay cores, but once this initial resistance is overcome the relay cores snap to their opposite position.

So far as the structure described above is concerned, the operation is substantially as follows. When the parts are in the positions shown in full lines in Figure 10, the gas valve I88 has been turned on so that no gas is supplied to the burner 2. Consequently, the room temperature will fall, and as this occurs the thermostat coil I88 will swing'the thermostat blade or arm I88 toward the left as viewed in Figure 18 so that, at 70 room temperature under the conditions assumed, the arm I88, will move to its dotted line position and will engage the contact I88. This immediately establishes a circuit from one end of the secondary of the transformer 24 through the conductor I8I, the thermostat coil I84, the thermostat arm I88, the contact I88, the conductor I82, the relay coil section I88, the contact I18, the switch arm I11, and the conductor I88 back to the other side of the secondary of the transformer 28. This energizes the coil I88 and exerts a downward pull upon the core I18 which moves the bar I12 downwardly, carrying with it the other core "I and swinging the valve arm I8I to its "on position, shown in dotted lines. The

snap mechanism described above serves to secure.

a positive shifting of the-valve arm I8I from one position to another. The downward movement of the relay cores I 18 and HI automatically shifts the switch arm I11 to its dotted line position as shown in Figure 10 so that the outer end of the arm I11 now engages the contact I18 which is associated with the other relay coil I81.

Since the valve I88 is now open the boiler I will send up heat to the room or rooms and the temperature therein will rise. The rising temperature causes the thermostat arm I88, which was moved to its dottedline position by the falling temperature, away from the contact I88, but this is of no effect because the switch arm I 11 was drawn away from the contact I18 and shifted Into its dotted line position at the time that the valve I88 was. opened to admit gas to the burner. The room temperature then continues to rise until it has reached approximately 72" as registere'd by the room thermostat, and at this point the thermostat arm I88 has been shifted back to its full line position shown in Figure 10. At the one side of the secondary of the transformer. 28, through the thermostat coil I88. the arm I88, the contact I81, the connector I88, the relay coil I81, the contact I18, the switch arm I11 (dotted line position). and the conductor I88, back to the other end of the secondary of the transformer 24. As soon as the relay coil I81 is energized the relay cores I18 and I 1| are shifted, upwardly in Figure 10, back to the position as shown in full lines in Figure 10. This shuts off the valve I88 and again brings the switch arm I11 up against the contact I18, whereupon the control means is adapted to again start up the gas burner'iust as soon as the temperature within the room again falls to 78 and the thermostat arm I88 engages the contact I88.

Thus, according to the control means just described, the valve I88 is opened when the room be subject to the disadvantages mentioned in the first part of this specification. That is, the temperature would swing downwardly too far and upwardly too far for best comfort conditions and the room temperature would actually vary over a range exceeding the theoretical two degree temperature differential oi the thermostat I53.

According to theprinclples of the present invention I have provided an auxiliary control, ac-

tually forming a part of the control circuits just described and intimately associated therewith for controlling the position of the valve I50 in accordance with, not only room temperature, but also the temperature of the heating medium through which the boiler I or other source of heat sends heat up to the rooms or other space to be heated. In Figure 10 it will be observed that this auxiliary device is the same as the device T shown in Figure 1 with its leads 5| and 52 connected, respectively, with the conductors I and I82 and serving to by-pass the thermostat blade I55 and the contact I56. From the description of the device T shown in Figure i it will be remembered' that the boiler thermostat 05 serves to oscillate the mercury switch tube 50 at each period of 15 change in the temperature of the heating medium. It will also be remembered that the electrodes associated with the conductors 5i and 52 are disposed in the central portion of the switch tube 50 and are normally open except during the brief interval of time when the oscillation of the switch tube 50shifts the globule oi inercury contained therein from. one end to the other, the globule of mercury in passing the electrodes associated with the conductors 5I and 52 serving thereby to momentarily connect these conductors. Since these conductors are connected with the conductors [BI and I 82, it will be seen that wherever there is a 15 change, under the conditions assumed, in the temperature of the heating medium the conductors SI and I82 will be electrically connected. Now if the valve I50 has already been turned off by virtue of the temperature within the room descending to 72 and by the thermostat blade I55 previously engaging the contact I51 so as to bring the parts to their full line positions shown in Figure 10, the momentary connection of the conductors I6I and 7 I62 will have exactly the same effect as if the room temperature had descended to 70 to bring the thermostat arm I65 against the contact I56.

That is, as the globule of mercurypasses the.

electrodes within the switch tube 50, a circuit will be established from. one end of the secondary of the transformer 24 through the lower portion of the conductor I 6|, the conductors 5| and 52, the lower portion of the conductor I02, the upper relay coil I66, the contact I15, the switch arm I", and the conductor I80, back to the other endot the secondary of the transformer 26. This momentary short circuiting of the conductors I6I and I02 has the effect of again starting up the burner. However, if the room temperature is still at or above 72, the burner will be immediately shut on as, soon as the switch arm. I" engages the contact I I6. But if the room temperature has descended even slightly below 72, so as to move the thermostat arm I55 away from the contact I51, the burner will be kept on until the room temperature reaches 72', and then the arm I55 will engage the contact I57 and will energize the coil I61 which swings the valve arm I5I upwardly to shut oil the valve I56.

Thus, inwthis modification, at every 15 change in the temperature of the heating medium, the device T operates to start up the burner 2 if, for any reason, the room temperature has descended even slightly below the upper diiierential limit,

downwardly, this will carry with it the switch,

blade III which will engage the contact I16, but since the thermostat arm I55 is still in engagement with the contact I51, the relay IIi'I will immediately be energized to swing the switch arm I" and the valve arm I5I back to the position shown in full lines in Figure 10. However, by this time, the mercury switch tube 50 has completed its oscillation and the mercury is not in a position to short circuit the electrodes therein, and hence the valve I50 will remain shut oif until the temperature of the heating medium has changed another 15. It will be observed that the modification just described operates on what has been termed the descending principle. That is, as the room temperature descends from. above 72 to a point slightly below 72", then at certain thermal periods the control is adjusted to bring the burner back on, even though the lower thermostat diiierential has not yet been reached by the room temperature, and maintained in operation until the room temperature is again brought up to 72.

The principles of the present invention as il lustraed in this type of control may also be embodied therein when arranged on what has been termed the ascending principle. Referring now to Figure 11, it will be observed that the only difference between this figure and the showing in Figure 10 is that the thermostat device T, instead of being connected with the conductor I82, has been connected with the conductor I83. The result of this arrangement, the room temperature is maintained substantially at 70, for at every 15 interval of temperature change in the heating medium, the device T operates to shut off the burner by closing the valve I50, and the valve is not opened unless and until the room temperature falls to 70. Figure 11 in full lines shows er portion of the conductor I6I, the conductors 5| and 52, the lower portion of the conductor I83, the relay coil I61, the switch contact I16, the switch arm I", and back to the secondary of the transformer through the conductor I60. This energizes the relay coil I61, causing the same to draw up on the plunger or core I1 I, swinging the valve arm I5I and the switch blade I" to their "off" positions, shown in dotted lines. If, for

example, the room temperature has risen slightly above 70 so that the thermostat arm I55 leaves the contact I56, the switch arm I II will remain in its oil or dotted line position, to which it was moved by the energization of the relay coil I61 as Just described. If the room temperature remains even slightly above 70, any subsequent 7 

